High-pressure processing chamber for a semiconductor wafer

ABSTRACT

A processing chamber having an improved sealing means is disclosed. The processing chamber comprises a lower element, an upper element, and a seal energizer. The seal energizer is configured to maintain the upper element against the lower element to maintain a processing volume. The seal energizer is further configured to generate a sealing pressure in a seal-energizing cavity that varies non-linearly with a processing pressure generated within the processing volume. In one embodiment, the seal energizer is configured to minimize a non-negative net force against one of the upper element and the lower element above a threshold value. The net force follows the equation P 2 *A 2 −P 1 *A 1 , where P 2  equals the sealing pressure, P 1  equals the processing pressure, A 2  equals a cross-sectional area of the seal-energizing cavity, and A 1  equals a cross-sectional area of the processing volume.

RELATED APPLICATION

The present application is a continuation-in-part of the U.S. patentapplication Ser. No. 10/364,284, titled “High-Pressure ProcessingChamber for a Semiconductor Wafer,” and filed Feb. 10, 2003. The U.S.patent application Ser. No. 10/364,284, titled “High-Pressure ProcessingChamber for a Semiconductor Wafer,” and filed Feb. 10, 2003, is herebyincorporated by reference.

FIELD OF THE INVENTION

This invention relates to the field of processing chambers. Moreparticularly, this invention relates to a system and a method forreliably sealing a high-pressure processing chamber.

BACKGROUND OF THE INVENTION

A semiconductor device is fabricated by placing it in a processingchamber in which device layers are formed, processing residue isremoved, and other processing steps are performed on it. In addition,certain processing chambers are used for cleaning semiconductor wafersat supercritical temperatures and pressures.

Generally, processing chambers contain an upper element and a lowerelement. When the two elements are brought together, they form aprocessing volume in which a wafer is contained during processing.During processing, it is critical that the processing volume remainsealed so that it can be maintained at correct operating conditions,such as high-pressure, atmospheric, or supercritical conditions. Sealingthe processing volume from the outside environment also ensures that (a)the processed wafer is not exposed to contaminants, making it unusable,and (b) processing materials, such as harmful chemicals, introduced intothe processing volume are not released to the surroundings.

A processing volume is maintained by applying a sealing force tocounteract a processing force generated within the processing volumewhile the wafer is being processed. The processing force acts to forcethe upper element and the lower element apart, opening the processingvolume seal and breaking the processing volume. The sealing force may beproduced by a hydraulic piston. To ensure that the processing volume ismaintained regardless of the processing force, before the workpiece isprocessed the sealing force is set to the largest attainable processingforce. The sealing force remains at this level even if the largestattainable processing force is never reached or is reached for only asmall portion of the entire processing cycle.

Such processing chambers have several disadvantages. First, sealingcomponents that bear the highest attainable sealing force for anunnecessary length of time are prone to failure after repeatedapplications of the sealing force. Second, the large contact forces onthe sealing face produce particulates that are introduced into theprocessing volume and contaminate the wafer. Third, the equipment usedto pressurize the hydraulic fluids adds costs to the processing system,since the equipment is used to seal the processing chamber and not toprocess a wafer. Fourth, those systems that could be designed to replacehydraulic components with supercritical components using supercriticalprocessing materials are expensive. These systems require complicatedrecycling techniques because the supercritical processing materials mustbe expanded and pressurized before they can be reused.

Accordingly, what is needed is a processing system that (1) does notrequire a continuous excessive sealing force to maintain a processingvolume, (2) reduces the number of contaminants that may be introducedinto the processing volume, (3) uses elements already used in processingfor maintaining the processing volume seal, and (4) uses a smallenergizing volume so that the processing system is compact and operatesmore efficiently.

BRIEF SUMMARY OF THE INVENTION

The present invention is directed to a semiconductor processing systemthat maintains a processing volume using a sealing pressure that followsan algorithm for optimal sealing. In a first aspect of the presentinvention, the semiconductor processing system comprises an upperelement, a lower element, and a sealing means. The upper element and thelower element are configured to be brought together to form a processingvolume. The seal energizer is configured to maintain the upper elementagainst the lower element to maintain the processing volume. The sealenergizer is further configured to control a sealing pressure in aseal-energizing cavity that varies non-linearly with a processingpressure generated within the processing volume.

In one embodiment of the invention, the seal energizer is configured tominimize a non-negative net force against one of the upper element andthe lower element above a threshold value. The net force follows theequation P2*A2−P1*A1, where P2 equals the sealing pressure, P1 equalsthe processing pressure, A2 equals a cross-sectional area of theseal-energizing cavity, and A1 equals a cross-sectional area of theprocessing volume. Preferably, the seal energizer is configured tomaintain a difference P2−P1 substantially constant during a processingcycle. The seal energizer preferably comprises a first cavity and theseal-energizing cavity. The first cavity is coupled to theseal-energizing cavity. The seal energizer is configured so that a firstpressure generated within the first cavity generates a second pressurein the seal-energizing cavity larger than the first pressure.Preferably, the cross-sectional area A2 is larger than thecross-sectional area A1.

In another embodiment, the system further comprises a means forgenerating supercritical conditions coupled to the processing volume.The system can further comprise a CO₂ supply vessel coupled to theprocessing volume. Preferably, the upper element and the lower elementform a supercritical processing chamber. The seal energizer preferablycomprises a hydraulic piston coupled to the lower element and configuredto maintain the processing volume.

In a second aspect of the present invention, a method of maintaining aprocessing volume comprises generating a processing pressure within aprocessing volume and controlling a sealing pressure to form andmaintain a processing volume. During a processing cycle the sealingpressure is varied non-linearly with the processing pressure.Preferably, the sealing pressure is related to the processing pressureby the equation ΔF=P2*A2−P1*A1, where P2 equals the sealing pressure, P1equals the processing pressure, A2 equals a cross-sectional area of aseal-energizing cavity, and A1 equals a cross-sectional area of aprocessing volume. The sealing pressure is varied to maintain ΔF above athreshold value. A cross-sectional area of the processing volumepreferably is smaller than a cross-sectional area of the seal-energizingcavity. The step of generating a processing pressure preferablycomprises containing a high-pressure processing fluid in the processingvolume. The high-pressure processing fluid can comprise supercriticalcarbon dioxide. The step of controlling a sealing pressure preferablycomprises generating a hydraulic pressure in the seal-energizing cavity.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING

FIG. 1 illustrates a side cross-sectional view of processing system inan open position, in accordance with one embodiment of the presentinvention.

FIGS. 2A–C illustrate a top view, a side cross-sectional view, and abottom view, respectively, of a plate used to form both asealing-energizing cavity and a processing volume in accordance with thepresent invention.

FIG. 3 illustrates the processing system of FIG. 1 in a closed position.

FIG. 4 illustrates the processing system of FIG. 1 in a closed positionand a yoke and stand assembly.

FIG. 5 illustrates the processing system in an open position and theyoke and stand assembly, all of FIG. 4.

FIG. 6 illustrates a side cross-sectional view of a balancing cylinderin accordance with one embodiment of the present invention, duringnormal processing.

FIG. 7 illustrates the balancing cylinder of FIG. 6 during abnormalprocessing.

FIG. 8 illustrates a side cross-sectional view and schematic diagram ofa processing chamber and associated valve assembly in accordance withone embodiment of the present invention.

FIG. 9 illustrates a side cross-sectional view and schematic diagram ofa processing chamber and associated valve assembly in accordance withanother embodiment of the present invention.

FIG. 10 illustrates a side cross-sectional view and schematic diagram ofa processing chamber and associated valve assembly in accordance withanother embodiment of the present invention.

FIG. 11 illustrates a side cross-sectional view and schematic diagram ofa processing chamber and associated valve assembly in accordance withanother embodiment of the present invention.

FIG. 12 is a graph of Pressure/Force versus time, illustrating operatingconditions for one embodiment of the present invention.

FIG. 13 is a graph of force differential versus processing pressure,illustrating operating conditions for one embodiment of the presentinvention.

FIG. 14 is a flow chart illustrating operating steps for one embodimentof the present invention.

DETAILED DESCRIPTION OF THE INVENTION

The present invention is directed to a system for and method ofefficiently maintaining a processing volume during device processing.When a semiconductor wafer undergoes processing in a processing chamber,it is subjected to a range of processing temperatures and pressures. Forthe processing to be performed correctly—that is, for a semiconductorwafer to be processed without being exposed to contaminants—theprocessing volume must remain hermetically sealed during processing.Moreover, the processing volume should remain sealed using the minimumforce necessary.

As used herein, processing pressure refers to the pressure generatedwithin a processing volume during device processing, and accordingly mayvary during device processing. Processing force refers to the forcegenerated by the processing pressure and exerted against a face of theprocessing volume. Sealing pressure refers to the pressure generatedwithin a seal-energizing cavity (described below). Sealing force refersto the force generated by the sealing pressure and exerted against aface of the seal-energizing cavity. In accordance with the presentinvention, the sealing force counterbalances the processing force and isused to maintain the processing volume seal. Thus, as described below,to efficiently maintain the processing volume, the sealing force must beslightly larger than the processing force. Processing refers to (a)processes performed on a semiconductor device during various stages ofdevice fabrication including, but not limited to, cleaning, deposition,ion implantation, or any other type of processing performed on asemiconductor wafer, and (b) processes performed on devices other thansemiconductor wafers. Processing materials refer to any materials usedfor processing within the processing volume and include, for example,HCI, CO₂, and supercritical CO₂. Processing performed while a processingvolume is maintained is referred to as normal processing. Processingperformed while the processing volume is not maintained is referred toas abnormal processing. Processing volume seal refers to a seal used toform the processing volume. The processing volume seal is formed bycontacting surfaces of a sealing element and one of the upper elementand the lower element.

Embodiments of the present invention maintain the processing volume bycounterbalancing the processing pressure with the sealing pressure. Byensuring that (a) a surface area of a face of the sealing-energizingcavity is sufficiently larger than a surface area of a face of theprocessing volume, or (b) the sealing pressure is sufficiently greaterthan the processing pressure, the sealing force will be sufficientlylarger than the processing force. In this way, the processing volumeseal is maintained without pre-pressurizing the seal-energizing cavitywith the seal pressure necessary to create a force to counteract thehighest processing force. The sealing pressure is thus said to track orfloat with the processing pressure so that the sealing force is equal toor somewhat greater than the processing force. In this way, the forcescounterbalance to maintain the processing volume seal.

Embodiments of the present invention thus reduce the wear on thecontacting surfaces of the seal since the contact force of the seal facenever becomes excessive. In addition, the components subjected to thecounterbalancing forces do not need to be designed to withstand thetotal force of the sealing pressure. The components must only withstandthe sealing force that exceeds the counterbalancing process force.

Embodiments of the present invention also protect against equipmentdamage. For example, if a workpiece or other foreign object isinadvertently positioned between the sealing surfaces, the sealing faceswill not exert an inordinate force against the workpiece or otherforeign object, damaging the processing equipment. By ensuring that thesealing force is small in such circumstances, the amount of damage tothe processing equipment is reduced.

Embodiments of the present invention also advantageously ensure thatwhen the sealing pressure is below a threshold, such as when theseal-energizing cavity has a leak or has not been filled with a sealingfluid, the processing volume is vented in a predetermined manner. Thus,the processing materials are not dispersed to the surroundingenvironment.

Furthermore, embodiments of the present invention reduce the size of aseal-energizing cavity that must be energized in order to maintain theprocessing volume seal. Other embodiments can reduce the size of theseal-energizing cavity because the net force acting on it is reducedsince the sealing pressure balances, rather than greatly exceeds, theprocessing pressure. Thus, the processing volume can be maintained moreefficiently.

FIG. 1 illustrates a cross-section of a processing assembly 100 inaccordance with one embodiment of the present invention. FIG. 1illustrates the processing assembly 100 in an open position, in which asemiconductor wafer can be inserted or removed from the processingassembly 100 as described below. The processing assembly 100 comprises abalancing cylinder 170 coupled to a processing chamber 101. As describedin more detail below, the balancing cylinder 170 ensures both that (a)during normal processing, the processing volume 140 is securely sealed(i.e., is maintained) and (b) when a critical pressure is not maintainedin a seal-energizing cavity, the processing chamber 101 is vented sothat processing is suspended.

The balancing cylinder 170 comprises a piston 172, which divides acylinder cavity into an upper reservoir 171 and a lower reservoir 173.The housing 176 of the piston 172 has a vent hole 175. Thus, when thepiston 172 is slid a sufficient distance in the direction denoted by thearrow 1 in FIG. 1, the vent hole 175 is located in the lower reservoir173 so that the lower reservoir 173 is vented through the vent hole 175.The upper reservoir 171 has an aperture to which a first end of a firstpipe 180 is connected. The lower reservoir 173 has an aperture to whicha first end of a second pipe 181 is connected. The balancing cylinder170 is further configured to accept a pipe 190 having a first end and asecond end. The first end resides in the lower reservoir 173 and allowsfluid communication between an outside source and the lower reservoir173.

The processing chamber 101 comprises an upper element 110 and a lowerelement 150. The upper element 110 comprises a plate 120 that divides aninner cavity of the upper element 110 into a seal-energizing cavity 115and an upper process cavity 116. The upper element 110 is configured toaccommodate the pipe 180 such that a second end of the pipe 180 isoperatively coupled to the seal-energizing cavity 115. In this way, theseal-energizing cavity 115 is in communication with the upper reservoir171. Moreover, as described below, preferably a volume defined by theseal-energizing cavity 115 and the upper reservoir 171 is isolated.

The upper element 110 is configured to accommodate the pipe 181 suchthat a second end of the pipe 181 is in communication with the upperprocess cavity 116. The plate 120 is slidably mounted within the innercavity of the upper element 110 and contains a piston seal 125. Thus, asillustrated in FIG. 1, when the plate 120 is slid in the direction ofthe arrow 1, a volume of the seal-energizing cavity 115 is decreased anda volume of the upper process cavity 116 is increased. As depicted inFIG. 1, a cross-section of the plate 120 is in the shape of an invertedU. The end of the inverted -U is a sealing face 130 containing a sealingelement 131, such as an o-ring, described in more detail below. Thelower element 150 has an upper surface 156 coupled to a platen 155.

FIGS. 2A–C illustrate a top view, a side cross-sectional side view, anda bottom view, respectively, of the plate 120. FIG. 2A illustrates theplate 120 as viewed from the seal-energizing cavity 115. FIG. 2A showsan outer face 135 of the plate 120, which forms a surface of theseal-energizing cavity 115. The outer face 135 has a radius 134 and acorresponding surface area. FIG. 2B illustrates a cross-sectional sideview of the plate 120. FIG. 2B shows that a cross-section of the plate120 has an inverted U-shape. FIG. 2B indicates, by the arrow 132, aradius of an inner face 136 of the plate 120. The inner face 136 definesa surface of the processing volume (140, FIG. 3) when the processingassembly 100 is in a closed position. FIG. 2B further shows the sealingface 130 and the sealing element 131 contained within a sealing grooveon the sealing face 130, both described in more detail below. FIG. 2Cillustrates a bottom view of the plate 120, as seen from the processingvolume 140, FIG. 3. As illustrated in FIGS. 2A–C, the inner face 136 andthe outer face 135 are opposing faces of the plate 120. Preferably, asdepicted in FIGS. 2A–C, a surface area of the outer face 135 depicted bythe radius 134 is larger than a surface area of the inner face 136depicted by the arrow 132. In one embodiment, the inner face 136 and theouter face 135 are both substantially planar.

It will be appreciated that while FIGS. 2A–C depict the plate 120 ascircular, the plate 120 can have other shapes, geometrical andnon-geometrical. Furthermore, while FIGS. 2A–C depict the sealingelement 131 and thus its associated sealing groove (not shown) ascircular and located on the plate 120, it will be appreciated that thesealing element 131 and its associated groove can have other shapes,both geometrical and non-geometrical, and can be located on othercomponents in the processing assembly 100. For example, the sealingelement 131 and its associated groove can be located on the surface 156of the lower component (150, FIG. 1), on the platen (155, FIG. 1), or atother locations.

Referring to FIG. 3, in operation, a semiconductor wafer (not shown)that is to undergo processing is placed onto the platen 155 and, asdescribed below, the upper element 110 and the lower element 150 arebrought into contact to form a processing volume 140. The processingassembly 100 is now in the closed position. The processing volume 140 isdefined by the inner face 136 of the plate 120, the sealing ring 131,and a portion of the upper surface 156. The platen 155 is containedwithin the processing volume 140. As described in detail below, theprocessing volume 140 is maintained by generating a pressure within theseal-energizing cavity 115, forcing the plate 120 and thus the sealingring 131 against the surface 156 of the lower element 150, thus forminga processing volume seal. Processing materials are now introduced intothe processing volume 140 to process the semiconductor wafer. It will beappreciated that in accordance with the present invention, thesemiconductor wafer can be processed using any number and combination ofprocessing methods, including, but not limited to, vacuum, low-pressure,atmospheric, high-pressure, and supercritical processing, used incleaning, deposition, or other semiconductor fabrication steps.

FIG. 3 also shows a cross section 185A–B and 186A–B of a yoke 188 (FIG.4) that acts as an additional clamp to tightly couple the upper element110 to the lower element 150, helping to maintain the processing volume140 during processing. FIG. 3 illustrates a left upper arm 185A and aleft lower arm 185B of the yoke 188, which together secure one side ofthe processing chamber 101, and a right upper arm 186A and a right lowerarm 186B of the yoke 188, which together secure another side of theprocessing chamber 101. The left upper arm 185A and the left lower arm185B form part of a left arm 185 (FIG. 4). The right upper arm 186A andthe right lower arm 186B form part of a right arm 186 (FIG. 4).

FIG. 4 illustrates the processing chamber 101, the yoke 188, and a standassembly 250 used to support the processing assembly (100, FIG. 1). FIG.4 illustrates the processing chamber 101 of FIG. 3 in the closedposition. For simplification, FIGS. 4 and 5 do not show the balancingcylinder 170 or the pipes 180, 181, and 190. FIG. 4 illustrates how theyoke arms 185 and 186 collapse around the processing chamber 101 totightly couple the upper element 110 to the lower element 150. The yoke188 can have various structures known to those skilled in the art. Forexample, the yoke arms 185 and 186 can be wedge shaped so that as theyare moved in the direction denoted by the arrows 2 in FIG. 4, the upperelement 110 and the lower element 150 are pushed toward and securedagainst each other; and as the yoke arms 185 and 186 are moved in thedirection denoted by the arrows 3, the upper element 110 and the lowerelement 150 are separated.

It will be appreciated that structures other than a yoke can be used tomore securely clamp the upper element 110 to the lower element 150. Forexample, a T-bolt located on one of the upper element 110 and the lowerelement 150, and a nut, located on the other of the upper element 110and the lower element 150, can be used to provide additional structureto tightly couple the upper element 110 to the lower element 150 duringprocessing.

FIG. 4 also illustrates a stand assembly comprising a base 209, a bottomextension 207 coupled to the base 209 and upon which the yoke 188 isslidably mounted, thus allowing the height of the yoke 188 and theattached processing chamber 101 to be adjusted; a clamp 201 and weight203, which together provide an extra force on the center of theprocessing chamber 101 to keep the upper element 110 secured against thelower element 150; and a top extension 205, which allows for thesecuring and removal of the clamp 201 and the weight 203.

FIG. 5 illustrates the processing chamber 101 of FIG. 4 in an openposition, with the yoke 188 and the stand assembly 250. In FIG. 5, theweight 203 has been lifted from the clamp 201, the clamp 201 has beenlifted from the yoke 188, and the yoke 188 has been removed from theprocessing chamber 101 by moving it in the direction denoted by thearrows 3. The upper element 110 has been displaced from the lowerelement 150 so that a semiconductor wafer can be inserted into orremoved from the processing chamber 101.

FIG. 3 is again referred to, to explain the operation of one embodimentof the present invention. In operation, a semiconductor wafer (notshown) is placed onto the platen 155. The upper element 110 is broughtinto contact with the lower element 150, and the yoke arms 185A–B and186A–B are positioned to tightly hold the upper element 101 to the lowerelement 150. Next, a sealing material such as an incompressible ornearly incompressible fluid, such as water, is introduced into the upperreservoir 171 of the balancing cylinder 170 and thus flows into thesealing cavity 115. It will be appreciated that other incompressiblefluids, such oil, can be used as a sealing material. In addition,materials other than an incompressible or nearly incompressible fluidcan be used in accordance with the present invention. It will also beappreciated that the incompressible or nearly incompressible fluid canbe introduced at any time before processing, such as, for example, whenthe processing assembly 100 is in the open position.

Next, a processing material is introduced into the lower reservoir 173.The processing material can, for example, be a cleaning material used indry cleaning, wet cleaning, supercritical cleaning, or any othercleaning method. Alternatively, the processing material can be anymaterial used to process a semiconductor or a non-semiconductor device.In one embodiment of the present invention, the cleaning material isCO₂, which is later brought to a supercritical state and used to cleanphotoresist residue from the surface of a semiconductor wafer in theprocessing volume 140. CO₂ can, for example, be introduced into thelower reservoir 173, through the pipe 190, which is later capped. TheCO₂ travels through the pipe 181, and then into the processing volume140. The CO₂ can then be brought to a supercritical state once insidethe processing volume 140 to form supercritical CO₂. The supercriticalCO₂ can then by cycled through the processing volume 140 to clean asemiconductor wafer residing on the platen 155.

The operation of the supercritical chamber and the use of supercriticalCO₂ are taught in U.S. patent application Ser. No. 09/912,844, titled“Supercritical Processing Chamber for Processing Semiconductor Wafer,”and filed Jul. 24, 2001; U.S. patent application Ser. No. 10/121,791,titled “High Pressure Processing Chamber for Semiconductor SubstrateIncluding Flow Enhancing Features,” and filed Apr. 10, 2002; and U.S.patent application Ser. No. 09/704,641, titled “Method and Apparatus forSupercritical Processing of a Workpiece,” and filed Nov. 1, 2000, all ofwhich are hereby incorporated by reference in their entireties.

As discussed above, the present invention ensures that the processingvolume (140, FIG. 3) is maintained during processing. FIG. 6 is a moredetailed schematic of the balancing cylinder 170 of FIGS. 1 and 3,illustrating the balancing cylinder 170 when the processing volume (140,FIG. 3) is maintained, that is, during normal processing. As describedin more detail below, with respect to FIGS. 6 and 7, the balancingcylinder 170 can be used to ensure that the processing volume 140 ismaintained while a semiconductor device is being processed within theprocessing volume 140. As illustrated in FIG. 6, the upper reservoir 171contains an incompressible fluid 177 such as water or oil. Theincompressible fluid 177 flows through the pipe 180 and completely orpartially fills the seal-energizing cavity (e.g., 115, FIG. 3).Preferably, a volume defined by the upper reservoir 171 and theseal-energizing cavity (115, FIG. 3) is isolated. Preferably, a cleaningfluid 178 that can be taken to a supercritical state is introduced intothe pipe 190, where it completely or partially fills the lower reservoir173 and is thus introduced into the processing volume 140 of the closedprocessing chamber 101. During processing, the cleaning fluid 178 isbrought to a supercritical state so that a semiconductor wafer in theprocessing volume 140 is cleaned. It will be appreciated that the stepsof introducing a fluid and bringing it to a supercritical or otherprocessing state can occur any number of times in any number ofprocessing cycles. During operation, the piston 172 is positioned sothat it blocks the aperture 175.

The balancing cylinder 170 advantageously ensures that the processingvolume 140 is tightly sealed. It achieves this by balancing theprocessing pressure within the processing volume 140 with the sealingpressure in the seal-energizing cavity 115. In one example, referring toFIGS. 3 and 6, the processing pressure is larger than the sealingpressure. Because the seal-energizing cavity 115 is in communicationwith the upper reservoir 171 through the pipe 180, the pressures withinboth are equal; and because the processing volume 140 is incommunication with the lower reservoir 173 through the pipe 181, thepressures within both are equal. Hence, when the processing pressure isgreater than the sealing pressure, the piston 172 is forced in thedirection indicated by the arrow 4 (FIG. 6). Because the volume definedby the upper reservoir 171 and the seal-energizing cavity (115, FIG. 3)is isolated, this motion in the direction of the arrow 4 increases thesealing pressure and decreases the processing pressure. This continuesuntil the processing pressure equals or balances the sealing pressure.Likewise, when the processing pressure is less than the sealingpressure, the piston 172 is forced in the direction indicated by thearrow 5 (FIG. 6), decreasing the sealing pressure and increasing theprocessing pressure. Again, this continues until the processing pressureequals or balances the sealing pressure because the fluid in the upperreservoir is incompressible or nearly incompressible. Thus, theprocessing pressure balances or tracks the sealing pressure and thesealing pressure does not have to be pre-loaded to the maximum possibleprocessing pressure.

FIG. 7 is a more detailed schematic of the balancing cylinder 170 ofFIG. 6, when an adequate pressure is not maintained in theseal-energizing cavity (115, FIG. 3), that is, during abnormalprocessing. This may occur for several reasons. For example, theseal-energizing cavity 115 may have a leak and therefore cannot retainthe incompressible fluid 177 received from the upper reservoir 171. Or,the upper reservoir 171 and hence the seal-energizing cavity 115 mayhave inadvertently not been filled with the incompressible fluid 177. Inany case, if the seal-energizing cavity 115 does not have sufficientpressure (that is, the sealing pressure falls below a thresholdpressure), the semiconductor cleaning process can be compromised.Because the processing volume 140 is not maintained, the processingmaterial 178 will leak from the processing volume (140, FIG. 3) duringprocessing, and external particles may enter the processing chamber,contaminating the semiconductor wafer. Embodiments of the presentinvention ensure that this does not occur.

As illustrated in FIG. 7, when the sealing pressure falls below athreshold value, the piston 172 is moved in the direction indicated bythe arrow 4. The piston vent hole 175 is now located in the lowerreservoir 173, and the processing material 178 is vented through thevent hole 175 and safely routed to a vessel (not shown), to the air, orto some other container in which it can be stored. Thus, the processingmaterial 178 does not enter the processing volume 140, and thesemiconductor processing is not compromised. Moreover, the ventingprocess can transmit a signal used to stop or suspend device processing.

FIGS. 8–10 illustrate embodiments comprising a pressure intensifier,which receives a low pressure in a low-pressure chamber and intensifiesit to produce a larger sealing pressure. Accordingly, the embodiments inFIGS. 8–10 require that a relatively small pressure be generated andmaintained to produce the sealing pressure. These embodiments thusrequire less energy and space to maintain a processing volume andaccordingly are more efficient.

By using a pressure intensifier to pressurize an incompressible fluidsuch as water, for example, to the necessary sealing pressure, the needfor high-pressure hydraulic equipment is eliminated. The pressure in thepressure intensifier is selected to be low enough so that thesupercritical process fluid will expand to the gas phase as it entersthe pressure intensifier. As the supercritical process fluid expands tothe gas phase, its density decreases and the mass of the process fluidrequired by the pressure intensifier to pressurize the incompressiblefluid to the required sealing pressure is less than if theintensification were not used. Such as structure advantageouslydecreases the cost of the process fluid that must be input into aprocessing system to maintain a processing volume seal and thusincreases the efficiency of the processing system.

FIG. 8 is a side cross-sectional view and schematic diagram of aprocessing assembly 300 comprising a processing chamber and associatedvalve assembly in accordance with one embodiment of the presentinvention. The processing assembly 300 comprises a processing chamber700; a CO₂ supply vessel 360; a seal-leak detector 340; a water vessel320; a drainage port 321; air-operated valves 323, 324, 325, 330, 342,and 343; a water filter 322; a pressure-ratio safety valve 341; anelectronic controller 350; pressure transducers 370 and 375; a set-pointsignal source 379; vents 362 and 371; a pressure regulator 352; and apressure relief valve 331. In one embodiment, the electronic regulator350 is an electronic pressure controller such as the ER3000,manufactured by Tescom Corporation, Elk River, Minn.

The processing chamber 700 comprises an upper element 302 and a lowerelement 304. The upper element 302 has an inner surface 301. The lowerelement 304 comprises an upper volume 406, a seal-energizing cavity 410,and a pressure intensifier 908. The lower element 304 contains apedestal 305. The pedestal 305 comprises a platen 306 contained in theupper volume 406 and a base 980 contained in the seal-energizing cavity410. The platen 306 has a stem slidably mounted in a neck 315, allowingthe pedestal 305 to slide upward, in the direction of the arrow 6, anddownward, in the direction of the arrow 7. The platen 306 contains asealing element 520. Preferably the sealing element 520 comprises agasket such as an o-ring. The height of the sealing element 520 withrespect to the other components is exaggerated for ease of illustration.FIG. 8 further illustrates a semiconductor wafer 400 resting on theplaten 306.

As illustrated in FIG. 8, the water vessel 320 is coupled to theair-operated valve 323, which is coupled to the water filter 322. Thewater filter 322 is coupled to the air-operated valve 325, which iscoupled to the seal-energizing cavity 410. The drainage port 321 iscoupled to the air-operated valve 325, which is coupled to theseal-energizing cavity 410. The leak detector 340 is coupled to the neck315 and a piston seal 809. The pressure ratio safety valve 341 iscoupled to the processing volume 510, the vent 362, the air-operatedvalve 343, and the pressure intensifier 908. The pressure relief valve331 is coupled to the vent 370, the air-operated valve 330, the pressuretransducer 375, and the pressure regulator 352. The air-operated valve330 is coupled to the pressure intensifier 908, the vent 370, thepressure-relief valve 331, the pressure transducer 375, and the pressureregulator 352. The electronic regulator 350 is coupled to the set-pointsignal source 379, the pressure transducer 375, and the pressureregulator 352. The CO₂ supply vessel 360 is coupled to the pressureregulator 352 and, through the air-operated valve 343, to the processingvolume 510. The pressure transducer 371 is coupled by the air-operatedvalve 342 to both the vent 362 and the pressure ratio safety valve 341.

The pressure intensifier 908 comprises a low-pressure chamber 705; aneck 303 having a cross-sectional area smaller than a cross-sectionalarea of the low-pressure chamber 705; a piston 310 having a base 392contained within the low-pressure chamber 705 and a head 391 containedwithin the neck 303; and a piston seal 809. The neck 303 is incommunication with the seal-energizing cavity 410, such that when thehead 391 is moved upward, in the direction of the arrow 6, a pressurewithin the seal-energizing cavity 410 is increased. Preferably, the base392 has a cross-sectional area larger than a cross-sectional area of thehead 391.

FIG. 8 illustrates the processing chamber 700 in a closed position. Aprocessing volume 510 is defined by the inner surface 301, the sealingelement 520, and an inner surface of the platen 306. As illustrated inFIG. 8, the sealing element 520 is preferably positioned within theplaten 306 so that a cross-sectional area of the processing volume 510is less than a cross-sectional area of the platen 306. A processingvolume seal is thus formed by the inner surface 301 and the sealingelement 520.

When the base 980 is moved upward, the sealing element 520 is forcedagainst the surface 301, placing the processing assembly 300 in theclosed position. In the closed position, the processing volume 510 isformed. When the base 980 is moved downward, the sealing element 520 isdisplaced from the surface 301, placing the processing assembly 300 inan open position. In the open position, the processing volume 510 isbroken so that a semiconductor wafer 400 can be inserted onto andremoved from the platen 306.

As described in more detail below, when the processing assembly 300 isin the open position, a semiconductor wafer is placed on the platen 306.A sealing material is then introduced into the seal-energizing cavity410 to move the pedestal 305 and thus the platen 306 in the direction ofthe arrow 6. The processing assembly 300 is now in the closed position.The pressure intensifier 908 can then be used to ensure that, while thesemiconductor wafer is being processed in the processing volume 510, aprocessing volume seal (and thus the processing volume 510) ismaintained. When processing is complete, the sealing material can beremoved from the seal-energizing cavity 410 to move the processingassembly 300 to the open position. The semiconductor wafer can then beremoved from the platen 306. It will be appreciated that devices otherthan semiconductor wafers can be processed in accordance with thepresent invention.

In operation, the processing assembly 300 is placed in the closedposition by introducing low-pressure water from the water vessel 320into the seal-energizing cavity 410. The low-pressure water travels fromthe water vessel 320, through the air-operated valve 323, the waterfilter 322, the piping 915 and 918, the air-operated valve 325, thepiping 916, and into the seal-energizing cavity 410. The low-pressurewater enters the seal-energizing cavity 410 between the head 391 and thebase 980. As the low-pressure water flows into the seal-energizingcavity 410, the water displaces the base 980 upward and displaces thehead 391 downward. Displacing the base 980 upward causes the sealingelement 520 to press against the upper surface 301, thereby forming theprocessing volume 510. The processing assembly 300 is now in the closedposition. When position sensors (not shown) detect that the platen 360has moved upward to form the processing volume 510 and that the head 391has moved downward to its limit (e.g., against the piston seal 809), theair-operated valves 323 and 325 close to isolate the seal-energizingcavity 410, now filled with low-pressure water.

Using a low-pressure material such as low-pressure water advantageouslyrequires a relatively small amount of energy to quickly fill theseal-energizing cavity 410. In other words, because the water flows intothe seal-energizing cavity 410 at low pressure, the components thatsupply water are not required to transfer and hold high-pressure water.The processing assembly 300 thus operates more efficiently than would aprocessing assembly that uses high-pressure equipment to fill theseal-energizing cavity 410 and thus form the processing volume 510.

Once the processing assembly 300 is in the closed position, low-pressureCO₂ gas is introduced from the CO₂ supply vessel 360 into thelow-pressure chamber 705. The CO₂ gas travels from the CO₂ supply vessel360, through the pressure regulator 352, through the piping 901C, theair-operated valve 330, the piping 901A, and into the low-pressurechamber 705. The introduction of the CO₂ gas into the low-pressurechamber 705 exerts a force on the piston 310 which pushes the base 392and thus the head 391 upward, in the direction of the arrow 6. Since thelow-pressure water above the head 391 is isolated, it cannot flow out ofthe seal-energizing cavity 410. The low-pressure water becomespressurized and pushes the head 391 and thus the platen 306 upward,forcing the sealing element 520 against the surface 301 to maintain theprocessing volume 510.

Next, during a device processing step, CO₂ is introduced into theprocessing volume 510, thus increasing the processing pressure. The CO₂travels from the supply vessel 360, through the air-operated valve 343over the piping 900A, and into the processing volume 510. The set pointsignal source 379 is set to a process pressure set point, which equalsthe desired processing pressure. The pressure transducer 370 monitorsthe processing pressure. When the pressure transducer 370 detects thatthe processing pressure equals the process pressure set point, itgenerates a signal transmitted to the air-operated valve 343 to stop theflow of CO₂ into the processing volume 510.

The processing pressure is now set to the desired operating pressure andthe semiconductor wafer can now be processed. The processing forcegenerated by the processing pressure is counterbalanced by the sealingforce as now described.

The pressure transducer 370 monitors the processing pressure andtransmits a related processing signal to the electronic controller 350.The pressure transducer 375 monitors an intensifier pressure generatedwithin the low-pressure chamber 705 and transmits a related sealingsignal to the electronic controller 350. If the processing signal andthe sealing signal indicate that the processing pressure is greater thanthe sealing pressure, the electronic controller 350 sends a signal tothe pressure regulator 352. The pressure regulator 352 now routes CO₂from the CO₂ supply vessel 360 to the low-pressure chamber 705, thusincreasing the intensifier, and thus the sealing, pressure.

The electronic controller 350 also ensures that the sealing forcecounterbalances the processing force when the processing pressure setpoint is changed. For example, if a lower processing pressure isdesired, the processing pressure set point can be decreased. Theair-operated valve 342 can be opened to decrease the processingpressure. The pressure transducer 370 detects this fall in processingpressure and sends a processing signal to the electronic controller 350.The electronic controller 350 then activates the pressure regulator 352to vent the low-pressure chamber 705 through the vent 362, thusdecreasing the intensifier pressure. Venting continues until the sealingforce equals the processing force.

When processing within the processing volume 510 is complete, theprocessing assembly 300 is placed in the open position. This isaccomplished by draining the low-pressure water in the seal-energizingcavity 410 through the piping 916 and 917, the air-operated valve 324,and out the drainage port 321. It will be appreciated that operation ofthe air-operated valves 323, 324, and 325 must be coordinated so that(a) low-pressure water is transferred from the water supply vessel 320and into the seal-energizing cavity 410 to place the processing assembly300 in the open position, and (b) low-pressure water is transferred fromthe seal-energizing cavity 410 and out through the drainage port 321 toplace the processing assembly 300 in the closed position.

During processing, CO₂ can be circulated within the processing volume510 to clean the surface of the semiconductor wafer 400. Later, theair-operated valve 343 can be opened so that the CO₂ used within theprocessing volume 510 can be returned to the CO₂ supply vessel 360 andused in a subsequent processing step. It will be appreciated that CO₂can be cycled through the processing volume 510 alone or in combinationwith other processing materials in one or more process cycles.

The pressure ratio safety valve 341 functions similarly to the balancingcylinder 170 of FIGS. 1 and 6. The pressure ratio safety valve 341contains a piston 333. The piston 333 moves to further balance theprocessing pressure and the intensifier such that the intensifierpressure, when multiplied by the pressure intensifier 908 produces apressure that generates a sealing force that equals or approximatelyequals the processing force, thus maintaining the processing volume 510.If the pressure within the low-pressure chamber 705 falls below thisvalue (the low-pressure point), the processing volume 510 is ventedthrough the piping 900A, 900B, and 900C, and out through the vent 362.The pressure ratio safety valve 341 thus complements the valve assemblyto counterbalance the processing force with the sealing force, thusmaintaining the processing volume 510.

Now the safety mechanisms of the processing assembly 300 are discussed.The pressure relief valve 331 ensures that the intensifier pressurenever exceeds a threshold pressure. If the intensifier pressure exceedsthe threshold pressure, the pressure relief valve 331 opens to vent thelow-pressure chamber 705 through the piping 901A, 901C, 901D, and 902,and out the vent 370. The seal-leak detector 340 monitors the pistonseal 809 and the neck 315. If a leak in either occurs, the seal-leakdetector 340 can take preventive actions such as, for example,energizing a flashing light to warn an operator, disabling theprocessing assembly 300 so that processing is interrupted, or takingother action.

FIG. 9 illustrates a side cross-sectional view and schematic diagram ofa processing assembly 400 in accordance with another embodiment of thepresent invention. The processing assembly 400 differs from theprocessing assembly 300 in FIG. 8 in that the processing assembly 400uses an electronic pressure controller 800 to control the pressureregulators 801 and 802. Compared to FIG. 8, like-numbered elementsperform similar functions. The processing assembly 400 comprises apressure transducer 380, the electronic pressure controller 800, thepressure regulators 801 and 802, and a set-point signal source 810. Thepressure transducer 380 is coupled to the processing volume 510, theelectronic pressure controller 800, and the pressure regulator 801. Theelectronic pressure controller 800 is coupled to a set-point source 810and the pressure regulators 801 and 802.

The electronic pressure controller 800 controls both the processingpressure and the intensifier pressure. The electronic pressurecontroller 800 uses a set point determined by the set point signalsource 810 to control the pressure regulators 801 and 802. The pressureregulator 801 controls the processing pressure, and the pressureregulator 802 controls the intensifier pressure. The processing assembly400 will vent both the processing volume 510 and the low-pressurechamber 705 if the pressure in the processing volume 510 exceeds aprocess set point. The electronic pressure controller 800 enables morecontinuous and precise control of the processing pressure than ispossible with the structure illustrated in FIG. 8.

FIG. 10 illustrates a side cross-sectional view and schematic diagram ofa processing assembly 500 in accordance with another embodiment of thepresent invention. The processing assembly 500 differs from theprocessing assembly 300 of FIG. 8 in that the processing assembly 500uses an electronic pressure controller 900 to control a pressureregulator 902, which controls the intensifier pressure. Compared to FIG.8, like-numbered elements perform similar functions. The processingassembly 500 comprises a pressure transducer 385, the electronicpressure controller 900, pressure regulators 901 and 902, and aset-point signal source 909. The pressure transducer 385 is coupled tothe processing volume 510, the pressure regulator 901, and theelectronic pressure controller 900. The electronic pressure controller900 is also coupled to the set-point signal source 909 and the pressureregulator 902. The pressure regulator 901 is coupled to the CO₂ supplyvessel 360, the processing volume 510, the vent 362, the pressure-ratiosafety valve 341, the low-pressure chamber 705, and the air-operatedvalve 330. The pressure regulator 902 is coupled to the CO₂ supplyvessel 360, the air-operated valve 330, and the pressure-relief valve331.

The electronic pressure controller 900 uses an external set point fromthe set-point signal source 909. The electronic pressure controller 900sends a signal to the pressure regulator 902, which controls theintensifier pressure. As the intensifier pressure rises to generate aforce to counterbalance the force generated by the processing pressure,a pressure signal from the pressure intensifier 908 is transmitted tothe pressure regulator 901, causing the processing pressure to track thesealing pressure. The processing pressure is monitored by a pressuretransducer 385 coupled to the electronic pressure controller 900.

In yet another variation (not illustrated), a pressure regulator with anelectronic pressure controller that responds to an external set pointmonitors the processing pressure and modulates a pressure regulator thatcontrols the sealing pressure. The modulation ensures that the sealingpressure tracks the processing pressure.

FIG. 11 illustrates a side cross-sectional view and schematic diagram ofa processing system 600, in accordance with another embodiment of thepresent invention. The processing system 600 comprises a processingchamber 920 having a top plate 921 and a bottom plate 922; apins-position sensor 925; a platen 982 containing a plurality of pins(not shown); a pedestal-position sensor 926; a pedestal 981 coupled to apiston 965; a differential pressure switch 932; a pressure switch 933; aseal energizer 950; a pressure intensifier 975; a pressure regulatorunit 944 having inputs 9440, 9441, and 9444 and outputs 9442 and 9443;an air-operated valve 952; pressure transducers 930, 931, and 934;pressure relief valves 945, 947, and 968; a filter 961; a solenoidcontrol valve 960; a solenoid control valve 951 having an output 9510and inputs 9511 and 9512; a directional flow controller 966; a vent 971;a hydraulic fluid vessel 967; compressed air supplies 972 and 999; andan external set point 946.

The top plate 921 and the bottom plate 922 define a processing volume983 containing the platen 982. The top plate 921 has an inner surface989 that forms part of the processing volume 983. The platen 982supports a workpiece such as a semiconductor wafer (not shown)undergoing processing within the processing volume 983. The piston 965has a head 962 with a face 9502. The head 962 is contained within aninner cavity 9501, as described below.

The directional flow controller 966 comprises a check valve 963 and aneedle valve 964. The pressure intensifier 975 comprises a low-pressurechamber 942, a high-pressure chamber 941, and a piston 943 coupling thelow-pressure chamber 942 to the high-pressure chamber 941. The pressureintensifier 975 has an input 9750 coupled to the low-pressure chamber942, and an output 9751 coupled to the high-pressure chamber 941.Similar to the pressure intensifier 908 of FIG. 8, a low-pressuregenerated at the input 9750 is translated into a high-pressure generatedat the output 9751. In one embodiment, the pressure regulator unit 944comprises a MAC PPC93A, sold by TSI Solutions, 2220 Centre Park Court,Stone Mountain, Ga. 30087. Tn one embodiment, the filter 961 is athree-micron filter.

The output 9751 of the pressure intensifier 975 is coupled to thedirectional flow controller 966, and is thus coupled to an input of thecheck valve 963 and an input of the needle valve 964. An output of thedirectional flow controller 966, and thus an output of the check valve963 and an output of the needle valve 964, is coupled to the pressurerelief valve 945. The pressure relief valve 945 is coupled to the filter961 and the solenoid control valve 960. An output of the solenoidcontrol valve 960 is coupled to the filter 961. The filter 961 iscoupled to the hydraulic fluid vessel 967, used to supply low pressurehydraulic oil. An output of the solenoid control valve 960 is coupled tothe differential pressure switch 932 and to the seal energizer 950. Aninner cavity 9501 (the seal-energizing cavity) of the seal energizer 950is coupled by piping to an output 9510 of the solenoid control valve951. Also coupled to the piping is the pressure relief valve 968. Afirst output 9511 of the solenoid valve 951 is coupled to an output ofthe air-operated valve 952. An input of the air-operated valve 952 iscoupled to the compressed air supply 972. A second output 9512 of thesolenoid valve 951 is coupled to the vent 971.

As illustrated in FIG. 11, the processing volume 983 is coupled to thepressure transducer 931 and the differential pressure switch 932. Afirst input 9440 of the pressure regulator unit 944 is coupled to thepressure transducer 931, a second input 9441 of the pressure regulatorunit 944 is coupled to an external set point 946, and a third input 9444of the pressure regulator unit 944 is coupled to the compressed airsupply 999. A first output 9442 of the pressure regulator unit 944 iscoupled to the pressure relief valve 947 and to the atmosphere through avent (not shown). A second output 9443 of the pressure regulator unit944 is coupled to the input 9750 of the pressure intensifier 975. Thepressure relief valve 947 is coupled to the input 9750 of the pressureintensifier 975 by piping, to which is also coupled the pressuretransducer 934. The pressure transducer can thus be used to monitor thepressure between the air-operated valve 947 and the input 9750 of thepressure intensifier 975.

In operation, a workpiece (not shown) is placed on pins (now shown)extending from the surface of the platen 982. The workpiece can beplaced on the surface of the platen 982 by retracting the pins, andlater, removed from the surface by extending the pins. The relation ofthe pins to the platen surface are monitored by the pins-position sensor925. The use of pins are taught, for example, in U.S. patent applicationSer. No. 10/289,830, titled “High Pressure Compatible Vacuum Chuck forSemiconductor Wafer Including Lifting Mechanism,” filed Nov. 6, 2002,which is hereby incorporated by reference in its entirety.

Next, low-pressure oil is transmitted from the hydraulic fluid vessel967, through the input of the air-operated valve 960, and into theseal-energizing cavity 9501 to close the processing chamber 920, asdescribed above in relation to the processing assembly 300 of FIG. 8.Next, a processing material, such as supercritical CO₂, is introducedinto the processing volume 983 to process the workpiece. The pressurewithin the processing volume 983 (the processing pressure) is translatedinto an electrical signal by the pressure transducer 931. The electricalsignal is transmitted to the pressure regulator unit 944, whichgenerates a mechanical output signal, such as a corresponding pressure.In normal operation, the mechanical output signal is transmitted to theinput 9750 of the pressure intensifier 975. The pressure intensifier 975then generates a high pressure output on its output 9751. The highpressure output is transmitted through the directional flow controller966 and to the seal-energizing cavity 9501 to seal the processingchamber 920, as described above in relation to the processing assembly300 of FIG. 8.

During abnormal operation, the pressure relief valve 945 can be used tooperatively couple the output of the regulator unit 966 to the filter961 and thus to the hydraulic fluid vessel 967. Alternatively, duringabnormal processing, the solenoid control valve 960 can be used tooperatively couple the output of the regulator unit 966 to the hydraulicfluid vessel 967.

The pressure relief valve 947 functions as a fail-safe mechanism on thelow-pressure side of the pressure intensifier 975, venting the input9750 of the pressure intensifier 975 when the pressure on the input 9750reaches a preset value. The pressure relief valve 945 performs a similarfunction on the high-pressure side of the pressure intensifier 975,venting the output 9751 of the pressure intensifier 975 when thepressure on the output 9751 reaches a preset value.

As a workpiece undergoes processing within the processing volume 983,the processing pressure is translated by the pressure transducer 931into an electrical signal transmitted to the pressure regulator unit944. The pressure regulator unit 944 in turn, generates a low pressure,which is transmitted to the input 9750 of the pressure intensifier 975.The low pressure is approximately that pressure which, when transmittedto the input 9750 of the pressure intensifier 975 is translated to ahigh-pressure generated on the output 9751, generating a sealing forceapproximately equal to the processing force. In operation, the pressureregulator unit 944 compares the external set point 946 with anelectrical (feedback) signal from the pressure transducer 931. If theexternal set point 946 is smaller than the feedback signal, then thepressure regulator unit 944 vents the pressure intensifier 975 to theatmosphere through the pressure relief valve 947. If the external setpoint 946 is larger than the feedback signal, then the pressureregulator unit 944 routes compressed air from the compressed air supply999, to the input 9444 of the pressure regulator unit 944, through theoutput 9443, and into the input 9750 of the pressure intensifier 975. Inthis way, the sealing force is regulated to track the processing force.

It will be appreciated that the pressure relief valves 945, 947, and 968ensure that the pressure transmitted between components never exceedspredetermined values. It will also be appreciated that the pressuretransducers 930 and 934 can be used to display and thus monitor thepressure along piping used in the processing system 600.

Other configurations in accordance with the present invention can alsobe used to efficiently maintain a processing volume, such as theprocessing volume 983 in FIG. 11, by exploiting a relationship between aprocessing pressure and a sealing force. One embodiment of the presentinvention uses a formula that relates a processing pressure to a sealingforce and uses the formula to calculate the minimum sealing force. Bylimiting the sealing force to this minimum, a processing volume can bemaintained by advantageously using the minimum energy required.

It is believed that when (1) the first face of a plate and the secondface of the plate have unequal cross-sectional areas, and (2) thedifference between the pressure exerted on the first face and thepressure exerted on the second face is constant, then (3) the net forceon the plate is not constant, but varies. Thus, for example, when apressure P1 is exerted on a first face having a cross-sectional area A1,and a pressure P2 is exerted on a second face having a cross-sectionalarea A2, then the net force (ΔF) on the plate is given by Equation 1:ΔF=P2*A2−P1*A1  (1)ΔF corresponds to the additional force on one side of the plate than onthe other side of the plate. When a plate is perfectly counterbalanced,ΔF equals 0. It will be appreciated that when a plate is used to form aprocessing volume, by counterbalancing the plate (i.e., by keepingΔF≧0), a processing volume is maintained. When ΔF is larger than 0, theprocessing volume is maintained using a greater force than is necessary,requiring extra, unneeded energy.

Again referring to Equation (1), when A1 equals A2, ΔF equalsA1*(P2−P1)—that is, when the pressure difference P2−P1, ΔP, is constant,ΔF is constant. If ΔP is not constant, then ΔF varies linearly with ΔP.When A1 does not equal A2, then the relationship between ΔF and ΔP isdifferent, a relationship exploited by the present invention. Indeed, itis believed that the net force ΔF is not always proportional to thedifference P2−P1. Thus, for example, when A1=100 in², A2=200 in²,P2=3,000 lb-f/in², and P1=1600 lb-f/in², then the difference in pressure(P2−P1) or ΔP=3,000 lb-f/in²−1,600 lb-f/in²=1,400 psid (“psid” denotingpounds per square inch differential). The net force, ΔF, then equalsP2*A2−P1*A1=3,000 lb-f/in²*200 in²−1,600 lb-f/in²*100 in²=1,400 lbf-d(“lbf-d” denoting pound force differential). When, however, P1=2,500lb-f/in² and P2=1,100 lb-f/in², so that ΔP does not change (i.e.,remains 1,400 psid), ΔF then equals P2*A2−P1*A1=1,100 lb-f/in²*200in²−2,500 lb-f/in²* 100 in²=−30,000 lbf-d. Thus, even though ΔP remainsconstant, when the pressure changes, ΔF can change magnitude anddirection. It is believed that in a processing system, such as theprocessing system 600 in FIG. 11, ΔF varies with the pressure within aprocessing volume (P_(vol)), such as the processing volume 983.

As described below, embodiments of the present invention exploit thisrelationship to efficiently maintain a processing volume. Using theabove example, when P1 increases, ΔF increases. Referring to FIG. 11, P1corresponds to the pressure within the processing volume 983 (P_(vol))and P2 corresponds to a sealing pressure (P_(seal)). Thus, when P_(vol)increases, and ΔP is kept constant, ΔF unnecessarily increases. ΔF (andthus P_(seal)) can be reduced to conserve energy, while maintaining theprocessing volume. This non-linear relationship (P_(seal) does not haveto track P_(vol)) of reducing P_(seal) so that ΔF does not unnecessarilyincrease can be used to reduce the energy input into a processing systemused to maintain a processing volume. Energy can be introduced into theprocessing system at, for example, the input 9444 of the pressureregulator unit 944 of FIG. 11.

The discussion above and the graphs below describe a processing systemin which a pressure differential ΔP is substantially constant. Thislimitation is used primarily to simplify the discussion. It can also beused to simplify the algorithms that control the pressure regulator unit944. It will be appreciated that ΔP can vary in accordance withembodiments of the present invention.

FIG. 12 is used to explain the principles behind embodiments of thepresent invention. FIG. 12 is a Pressure/Force vs. Time Graph 1200 forthe processing system 600 of FIG. 11, for one or more processing cyclesat increasing times t₁, through t₈. The Graph 1200 has two verticalaxes, a left vertical axis and a right vertical axis. The left verticalaxis, labeled “Pressure,” in the units of psig or psid, is used tomeasure the values represented by the lines 210, 215, and 220, describedin more detail below. The right vertical axis, labeled “Force,” in theunits lbf or lbf-d, is used to measure the values represented by thelines 225, 230, and 235, also described in more detail below. It will beappreciated that while the Graph 1200 shows time on a horizontal axis,the Graph 1200 is used to explain the relationship between pressuredifferentials and force differentials, and thus could also be referredto as a Force versus Pressure graph.

Referring to FIG. 11, the processing system 600 comprises a processingvolume 983. The processing volume 983 is maintained by counterbalancing(1) a processing force exerted against a face 989 in the processingvolume 983 and (2) a sealing force exerted against the face 9502 of thehydraulic piston 965. ΔF corresponds to the additional force above thatneeded to maintain the processing volume 983. In one embodiment, theface 9502 has a larger cross-sectional area than the cross-sectionalarea of the face 989. Preferably, the processing system 600 isconfigured to perform high-pressure processing. For example, theprocessing system 600 can be configured to introduce supercritical CO₂into or generate supercritical CO₂ within the processing volume 983.Preferably, the processing volume 983 is thus configured to withstandsupercritical temperatures and pressures, and is coupled to a vessel forsupplying supercritical materials, such as a CO₂ supply vessel.

The Graph 1200 shows a Pressure vs. Time plot for 3 lines, using theleft vertical axis for measurement: the line 210, P_(vol) vs. time,where P_(vol) is measured in psig; line 215, P_(seal) vs time, whereP_(seal) is measured in psig; and line 220, ΔP vs time, where ΔP equalsP_(seal)−P_(vol), measured in psid. The Graph 1200 also shows a Forceversus Time plot for 3 lines: line 225, the force exerted against theface 989, in lbf, vs. time; line 230, the calculated hydraulic forceexerted against the face 9502, in lbf, vs. time; and line 235, ΔF vs.time, the difference between lines 225 and 230, the calculated sealforce, in lbf-d. The line 220 shows that when ΔP remains substantiallyconstant, ΔF decreases as the pressure decreases.

Table 1 lists some of the values used to plot the graph 1200 in FIG. 12.Referring to Table 1, column 2, labeled “Processing Pressure,” containsentries for P_(vol). Colunm 3, labeled “Sealing Pressure,” containsentries for P_(seal) sufficient to maintain the processing volume 983.Column 1, labeled “MAC Pressure,” contains entries for pressuresgenerated by the pressure regulator unit 944, which are translated intosealing pressures (P_(seal)) sufficient to generate a force sufficientto maintain the processing volume 983. Column 4, labeled “ΔP,” containsentries for the difference between corresponding entries in columns 2and 3 (ΔP=P_(seal)−P_(vol)). Column 5, labeled “Processing Force,”contains entries for the force exerted on the face 989. Column 6,labeled “Sealing Force,” contains entries for the force exerted on theface 9502. Column 7, labeled “ΔF,” contains entries for the differencebetween corresponding entries in columns 5 and 6.

FIG. 13 is a graph 1300, plotting the force differential ΔF, in theunits 1,000 lbf-d, versus the P_(vol), in psig, for some of the pointsin Table 1. The graph 1300 shows that when ΔP is substantially constant,ΔF varies directly with P_(vol). It will be appreciated that thisrelationship holds even when ΔP is not substantially constant, butvaries. For illustration, the graph 1300 shows processing pressuresbetween 28 psig and 1,218 psig, while ΔP is substantially constant,varying between 196 psid and 226 psid.

This relationship has two consequences. First, if there is a minimumforce necessary to maintain a processing volume (i.e., maintain aprocessing seal), ΔP must be selected so that at the lowest pressurethere is sufficient force to maintain the processing volume. In thiscase, as the pressure rises, the net force ΔF increases above thisminimum level (ΔF_(thresh) ^(LOW)), an inefficient process. Instead, thepressure regulator unit 944 can be optimized so that P_(seal) iscontrolled so that ΔF never exceeds (ΔF_(thresh) ^(UPP)), thus using theminimum energy to maintain the processing volume. The second consequenceis that, if the required sealing force (and thus P_(seal)) increases ata slower rate than the processing force (and thus P_(vol)), thenP_(seal) can lag behind P_(vol) and still maintain the processingvolume. Thus, the response time of the pressure regulator unit 944 usedto generate a sealing force need not be as fast as the changes inprocessing pressures.

TABLE 1 MAC Processing Sealing Pressure Pressure Pressure ΔP ProcessingSealing ΔF (psig) (psig) (psig) (psid) Force (lbf) Force (lbf) (lbf-d) 628 223 196 2,800 26,760 23,960 8 115 312 197 11,500 37,440 25,940 11 222421 199 22,200 50,520 28,320 14 359 559 200 35,900 67,080 31,180 19 543748 205 54,300 89,760 35,460 21 647 854 206 64,700 102,480 37,780 26 8191,020 202 81,900 122,400 40,500 29 963 1,171 209 96,300 140,520 44,22036 1,218 1,445 226 121,800 173,400 51,600 55 1,980 2,216 236 198,000265,920 67,920 64 2,308 2,559 251 230,800 307,080 76,280 75 2,817 2,982165 281,700 357,840 76,140

Again referring to FIG. 11, the pressure regulator unit 944 can becontrolled in accordance with the present invention to efficientlymaintain a processing volume using Equation (1) above to calculate aforce differential. For example, the pressure regulator unit 944 can beprogrammed or coupled to a controller that controls the pressureregulator unit 944 to efficiently vary P_(seal) (and thus the sealingforce) in accordance with the present invention. The pressure regulatorunit 944 can be programmed to generate a pressure that is ultimatelytranslated into the required P_(seal) and thus translated into thesealing force, as described above.

The pressure regulator unit 944 can also be controlled so that ΔF neverfalls below a threshold value, (ΔF_(thresh) ^(LOW)). (ΔF_(thresh)^(LOW)) can correspond, for example, to a force differential that allowsfor small pressure swings and thus ensures that a processing volume. ismaintained even if the pressure regulator unit 944 is slow to increaseP_(seal) in response to changes in P_(vol). It will be appreciated thatthe pressure regulator unit 944 must be configured to switch betweenpressures quickly enough to constantly maintain the processing volume983.

FIG. 14 shows sealing steps 1400 in accordance with one embodiment ofthe present invention. In the first step 1401, the start step, anyinitialization steps are performed. Referring to FIG. 11, in the firststep 1401 a wafer is placed on the platen 982 and the processing volume983 is formed. Other initialization steps can include determining themaximum processing pressure that will be attained within the processingvolume 983, calculating other processing parameters, etc. Next, in thestep 1402, it is determined whether a minimum force differential(ΔF_(thresh) ^(LOW)) is needed to maintain the processing volume 983. Ifa minimum force differential is necessary, step 1410 is performed;otherwise, step 1405 is performed.

In the step 1410, a minimum force differential is calculated. In thestep 1405, ΔF_(thresh) ^(LOW) is set to 0 lb-f. It will appreciated thatin the step 1405, the ΔF_(thresh) ^(LOW) can be set to another valueappropriate for the circumstances. After either the step 1410 or thestep 1405, the step 1415 is performed.

In the step 1415, a wafer is processed within the processing volume 983.Next, in the step 1420, P_(vol) and P_(seal) are read and P_(seal) isvaried to maintain the processing volume 983. In accordance with oneembodiment of the present invention, P_(seal) is varied in accordancewith the present invention to efficiently maintain the processing volume983. That is, P_(seal) can be set to lag P_(vol) and still maintain theprocessing volume 983 by ensuring that ΔF>ΔF_(thresh) ^(LOW). It will beappreciated that while, for simplicity, FIG. 14 shows the step 1420being performed after the step 1415, it will be appreciated that thestep 1420 will be performed during the step 1415, that is, while a waferis being processed.

Next, in the step 1430, it is determined whether processing of the waferis complete. If processing is not complete, the step 1420 is performedagain. If processing is complete, the step 1435 is performed. In thestep, 1435, the processing volume 983 is returned to non-processingconditions, the processing volume 983 is broken, and the wafer isremoved from the platen 982. Next, in the step 1440, the processingsteps are complete.

As described above, P_(seal) can be controlled by the pressure regulatorunit 944, which can be programmed to perform the step 1420, inaccordance with the present invention. As described above, the pressureregulator unit 944 can be programmed or otherwise controlled to generatea pressure that is translated into a sealing force as described inEquation (1) above.

It will be readily apparent to one skilled in the art that other variousmodifications may be made to the embodiments without departing from thespirit and scope of the invention as defined by the appended claims.

1. An apparatus for processing a semiconductor wafer, comprising: a. anupper element; b. a lower element, wherein the upper element and thelower element are configured to be brought together to form a processingvolume; c. a seal energizer that comprises a seal-energizing cavitycoupled to the upper element and configured to maintain the upperelement against the lower element by a sealing pressure generated withinthe seal-energizing cavity; and d. a pressure controller configured toautomatically non-linearly vary the sealing pressure to lag a processingpressure generated within the processing volume and maintain theprocessing volume during processing.
 2. The apparatus of claim 1,wherein the seal energizer is configured to apply a non-negative netforce against one of the upper element and the lower element above athreshold value, the net force following the equation P2*A2−P1*A1,wherein P2 equals the sealing pressure, P1 equals a pressure generatedwithin the processing volume, A2 equals a cross-sectional area of theseal-energizing cavity, and A1 equals a cross-sectional area of theprocessing volume.
 3. The apparatus of claim 2, wherein thecross-sectional area A2 is larger than the cross-sectional area A1. 4.The apparatus of claim 1, wherein the seal energizer further comprises afirst cavity, wherein the first cavity is coupled to the seal-energizingcavity, and the seal energizer is configured so that a first pressuregenerated within the first cavity generates a second pressure in theseal-energizing cavity larger than the first pressure.
 5. The apparatusof claim 1, further comprising a means for generating supercriticalconditions coupled to the processing volume.
 6. The apparatus of claim5, further comprising a CO₂ supply vessel coupled to the processingvolume.
 7. The apparatus of claim 1, wherein the upper element and thelower element form a supercritical processing chamber.
 8. The apparatusof claim 1, wherein the seal energizer comprises a hydraulic pistoncoupled to the lower element and configured to maintain the processingvolume.
 9. The apparatus of claim 1, wherein the pressure controller isprogrammed to maintain a difference between a sealing force and a forcegenerated within the processing volume within a preselected range. 10.The apparatus of claim 9, wherein a lower bound of the preselected rangeincludes a minimum force for maintaining the processing volume.
 11. Theapparatus of claim 10, wherein the minimum force is based on a delaybetween generating the sealing force and generating the force within theprocessing volume.
 12. The apparatus of claim 1, wherein the forcegenerated within the processing volume varies during a processing cycle.13. The apparatus of claim 1, wherein the pressure controller comprisesa pressure regulator.
 14. The apparatus of claim 13, further comprisinga pressure monitor coupled to the processing volume and to the pressureregulator.
 15. An apparatus for processing a semiconductor wafer,comprising: a. an upper element; b. a lower element coupled to aseal-energizing cavity, wherein the upper element and the lower elementare configured to be brought together to form a processing volume; andc. means for automatically non-linearly varying a sealing pressurewithin the seal-energizing cavity to maintain within a preselected rangea difference between a sealing force and a force generated within theprocessing volume, thereby maintaining the processing volume.
 16. Anapparatus for processing a semiconductor wafer, comprising: a. aprocessing chamber comprising a processing volume for processing thesemiconductor wafer by generating a processing pressure; and b. meansfor maintaining the processing volume by sensing the processing pressureduring processing and automatically generating a sealing pressure thatnon-linearly lags the sensed processing pressure.